1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a shield.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head section having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate. The write head section includes a main pole that produces a write magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head section of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium.
Here, the side of positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erasure). For higher recording densities, it is necessary to prevent adjacent track erasure.
Providing a write shield near the main pole is effective for preventing adjacent track erasure induced by the skew mentioned above and increasing the recording density. For example, U.S. Patent Application Publication Nos. 2005/0128637 A1 and 2010/0165517 A1 each disclose a magnetic head including a write shield having an end face that is located in the medium facing surface to wrap around an end face of the main pole.
A magnetic head including a write shield is typically provided with one or more return path sections for connecting the write shield to part of the main pole away from the medium facing surface. The write shield and the one or more return path sections have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, so as to prevent the magnetic flux from reaching the recording medium. The write shield and the one or more return path sections also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. The magnetic head including the write shield makes it possible to prevent adjacent track erasure and allows a further improvement of the recording density.
U.S. Patent Application Publication Nos. 2005/0128637 A1 and 2010/0165517 A1 each disclose a magnetic head including, as the aforementioned one or more return path sections, a return path section located on the leading side relative to the main pole and a return path section located on the trailing side relative to the main pole.
In general, a magnetic path including the write shield and one or more return path sections is formed as a magnetic structure including a plurality of magnetic layers. Now, a method for forming the plurality of magnetic layers constituting the magnetic structure will be discussed below. At least one of the plurality of magnetic layers constituting the magnetic structure forms the write shield. Each of the plurality of magnetic layers is formed by electroplating, for example. In a typical method for forming a magnetic layer by electroplating, a seed layer having conductivity is first formed on a surface of a structure on which the magnetic layer is to be formed. This seed layer will serve as the cathode for electroplating and as the seed for the magnetic layer to be formed by electroplating. Next, the structure with the seed layer formed thereon is immersed in an electrolytic the anode is provided. Then, using the anode and the seed layer serving as the cathode, the electrolytic solution is energized to form a plating film, which is to become the magnetic layer, on the seed layer.
The seed layer used in forming the magnetic layer in the aforementioned method constitutes part of the magnetic structure. The seed layer is preferably made of a magnetic material. In particular, to form a second magnetic layer on a first magnetic layer with the seed layer interposed therebetween, the seed layer is preferably made of a magnetic material.
Of the plurality of magnetic layers constituting the magnetic structure, the at least one magnetic layer that forms the write shield has an end face located in the medium facing surface. Another at least one magnetic layer that forms one or more return path sections may also have an end face located in the medium facing surface.
Here, a case will be contemplated where a first magnetic layer and a second magnetic layer that is formed on the first magnetic layer with a seed layer interposed therebetween each have an end face located in the medium facing surface. In this case, to form the magnetic layers by the above-described typical method employing electroplating, the seed layer interposed between the first and second magnetic layers is to have an end portion exposed in the medium facing surface.
A description will now be given of the problem with the case where a first magnetic layer and a second magnetic layer that is formed on the first magnetic layer with a seed layer interposed therebetween each have an end face located in the medium facing surface and the seed layer interposed between the first and second magnetic layers has an end portion exposed in the medium facing surface as mentioned above. If the seed layer is made of a material different from the material employed for the first and second magnetic layers, the seed layer should have features different from those of the first and second magnetic layers. Even if the same material is employed for the seed layer as that for the first and second magnetic layers, forming the seed layer by a method different from that for forming the first and second magnetic layers should make the seed layer have features different from those of the first and second magnetic layers in terms of film quality, crystal grain size, crystal structure, and the like. If the seed layer having features different from those of the first and second magnetic layers as mentioned above has an end portion present between the end face of the first magnetic layer and the end face of the second magnetic layer in the medium facing surface, magnetic field leakage from the inside to the outside of the magnetic structure tends to occur in the vicinity of the end portion of the seed layer. This may result in the occurrence of adjacent track erasure.
Aside from the aforementioned case, if the seed layer is relatively large in thickness and the end portion of the seed layer is adjacent to the end face of a magnetic layer in the medium facing surface, magnetic field leakage from the inside to the outside of the magnetic structure tends to occur in the vicinity of the boundary between the end face of the magnetic layer and the end portion of the seed layer. This may result in the occurrence of adjacent track erasure.